Lighting optical machine and defect inspection system

ABSTRACT

A lighting optical machine and defect inspection system having high reliability and safety when a laser beam is used as a light source. The lighting optical machine comprises: a housing, which accommodates a laser source, a beam polarization mechanism having first and second plane mirrors enabling a beam emitted from the laser source to be reflected so that the beam travels in the direction almost parallel to the beam emitted from the laser source, a beam expander for converting the beam to a parallel beam having a larger cross-sectional area, an objective lens, through which the parallel beam is reduced and applied to the surface of a sample; a first control mechanism for controlling the directions of the two plane mirrors of the beam polarization mechanism with an electric signal; and a second control mechanism for controlling the focus position of the beam expander with an electric signal.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The present invention relates to a lighting optical machine and adefect inspection system used for the inspection or observation ofcritical dimensional pattern defects and foreign matters typically foundin manufacturing processes of semiconductor devices or flat paneldisplays.

[0003] 2. Background Art

[0004] As semiconductors are highly integrated, circuit patterns tend tobe finer than ever. Under these circumstances, higher and higherresolution is required for detecting defects of circuit patterns onwafers, which are lithographed through exposure from circuit patternsformed on masks or reticles for use in photolithography processes formanufacturing semiconductors. In order to enhance the resolution, alighting beam may be changed from visible light to ultraviolet light sothat the beam has a shorter wavelength. Conventionally, an Hg lamp hasbeen used as a light source, and among various emission lines generatedfrom an Hg lamp, those with required wavelengths have been opticallyselected for use. However, the emission lines of the Hg lamp have abroader emission spectrum and it is difficult to correct optical coloraberrations thereof. Further, in order to obtain sufficient illuminance,a large light source is necessary, resulting in decreased efficiency.

[0005] In recent years, an exposure device carrying a KrF excimer laserwith a wavelength of 248 nm as a light source therefor in thesemiconductor manufacturing processes has been developed. However, theexcimer laser light source is large and predetermined safety measuresmust be taken due to the use of fluorine gas.

[0006] Examples of ultraviolet laser light sources include a laserdevice wherein the wavelength of a solid-state YAG laser light isconverted with a nonlinear optical crystal and an Ar—Kr laser device,and a laser beam with the wavelength of 266 or 355 nm can be obtainedthereby. It is advantageous that these laser devices have a largeroutput power in comparison with lamps conventionally used as lightsources, and generate a parallel pencil, the beam passage of which canfreely be routed. On the other hand, due to the coherence properties oflasers, laser speckle occurs, and causing adverse influences such asuneven brightness in detecting the circuit patterns formed on a sample.Incidentally, JP Patent Publication (Kokai) No. 2001-141428 A disclosesa solution to this problem as a conventional technology. However, thetechnology of the above publication is not directed at reliabilityregarding the detection accuracy, such as optical axis adjustment andluminous energy adjustment, or at safety during the use of a laser.

SUMMARY OF THE INVENTION

[0007] An object of the present invention is to provide a lightingoptical machine and a defect inspection system having high reliabilityand safety when a laser beam is used as a light source.

[0008] According to an embodiment of the present invention, a lightingoptical machine comprises:

[0009] a housing, wherein the housing accommodates a laser source, abeam polarization mechanism having a first and a second plane mirrors,which enable a beam emitted from the laser source to be reflected sothat the beam travels in the direction almost parallel to the beamemitted from the laser source, a beam expander for converting the beamto a parallel beam having a larger cross sectional area, and anobjective lens, through which the parallel beam is reduced and appliedto the surface of a sample;

[0010] a first control mechanism for controlling the directions of thetwo plane mirror of the beam polarization mechanism with an electricsignal; and

[0011] a second control mechanism for controlling the focus position ofthe beam expander with an electric signal,

[0012] A further embodiment of the present invention is a pattern defectinspection system provided with the above lighting optical machine.

[0013] This specification includes part or all of the contents asdisclosed in the specification and/or drawings of Japanese PatentApplication No. 2002-200720, which is a priority document of the presentapplication.

BRIEF DESCRIPTION OF THE INVENTION

[0014]FIG. 1 is a view showing the configuration of a lighting opticalmechanism according to the present invention.

[0015]FIG. 2 is a perspective view showing the configuration of amechanical part of an optical wafer defect inspection.

[0016]FIG. 3 is a perspective view showing the configuration of a lowcoherent optical unit 6.

DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will bedescribed with reference to FIGS. 1 to 3. FIG. 1 shows one exemplaryconfiguration of a lighting optical system according to the presentinvention. In the present invention, in order to accomplish highbrightness lighting in a short wavelength area, a far ultraviolet laserbeam is used as a laser beam source 3. A laser beam L1 emitted(oscillated) from the laser beam source 3 changes its angle at a firstplane mirror 4 a and changes its angle again at a second plane mirror 4b so as to be almost parallel to a beam emitted from the laser beamsource 3.

[0018] Next, a beam expander 5 enables the laser beam L1 to become aparallel pencil having a large cross-sectional diameter. The beam thenenters into an objective lens 11 through a low coherent optical unit, abeam splitter for polarization, polarization devices, or the like, withwhich an object to be measured is irradiated. The laser beam L1 expandedby the beam expander 5 is converged around the pupil of the objectivelens 11 with a lens on the way to the objective lens 11, and thereafterused for Kohler's illumination on a sample.

[0019] Further, the first and second plane mirrors 4 a and 4 b arecoupled to a beam polarization mechanism 40 a and 40 b, respectively,which are driven by a motor, etc. to change the angle of the planemirrors. Furthermore, they are connected to a beam polarizationmechanism control part 41 for controlling their angles. Moreover, thebeam polarization mechanism control part 41 is coupled to a manualoperation input part 42, through which the polarization angle can bemanually controlled.

[0020] In addition, the beam expander 5 is coupled to a beam expanderadjustment mechanism 50 driven by a motor, etc., and the beam can bechanged to a parallel pencil having an enlarged cross-sectional diameterby changing the focus position. Further, it is connected to a beamexpander adjustment mechanism control part 51 to control the size of thecross-sectional diameter. The beam expander adjustment mechanism controlpart 51 is connected to a manual operation input part 52, through whichthe size of cross-sectional diameter of the beam can be manuallycontrolled.

[0021] Also, a first beam splitter 30 a is provided after the beamexpander 5 for amplitude splitting of the parallel pencil, which isfurther divided in two with a second beam splitter 30 b. One of thedivided beams enters into a beam profile observation camera 31 so thatthe beam shape thereof is obtained. Using the obtained shape, the beamcross-sectional diameter can be measured. Thus, when the obtained valueis not that of a predetermined cross-sectional diameter, an instructionis sent to the beam expander adjustment mechanism control part 51 toadjust the cross-sectional diameter. Based on the instruction, the beamcross-sectional diameter is automatically adjusted to achieve thepredetermined value.

[0022] The other divided beam passes through a convergence lens 33 andis converged on a beam spot positioning sensor 32 so that a beamposition displacement is detected. When a position displacement isfound, an instruction to adjust the beam position to the center is sentto the beam polarization mechanism control part 41. Based on theinstruction, the beam spot position is automatically adjusted to thecenter. As described above, it is possible to maintain a constantlystable light beam.

[0023] Additionally, there may be provided a display monitor 60, whichmonitors information from the beam profile observation camera 31 andbeam spot positioning sensor 32, or a communication means 61.

[0024] All portions except the manual operation input parts 42 and 52are accommodated in a housing 62, and thereby there is no fear of alaser beam leaking outside. When the laser beam is adjusted, theposition, angle, or cross-sectional diameter of the beam can be adjustedwith the manual operation input parts 42 and 52 present outside thehousing 62, so that there is no chance that an operator may be exposedto the laser beam and the laser beam can be adjusted by remote control.The housing 62 may have a structure such as a shape for covering allportions except the manual input parts 42 and 52. It may also have ashape with sleeve-shaped members for covering beam passages and aslightly larger covering part for the lens, etc. Further, it is notnecessary to conduct operations in a limited narrow space, and anoperator can conduct operations through remote control, so that thelabor of the operator can be reduced. It is preferable to install thedisplay monitor 60 or communication means 61 outside the housing 62.

[0025] Next, FIG. 2 shows one exemplary configuration of a lightingoptical mechanism of an optical wafer defect inspection system as anapparatus provided with the above lighting optical machine. However, thefigure partially contains a flow chart regarding the image processingmechanism. In the present invention, a ultraviolet laser beam is used asa light source to achieve high brightness in a short wavelength area.

[0026] A stage 2 has degrees of freedom in directions of the X, Y, Z,and θ axes, and a semiconductor wafer 1 having one example pattern to beinspected is mounted as a sample. The laser beam L1 emitted from thelaser beam source 3 enters into the objective lens 11 through a mirror 4comprising a first plane mirror 4 a and a second plane mirror 4 b, abeam expander 5, a low coherent optical unit 6, a lens 7, a polarizationbeam splitter 9, and polarization devices 10. It is then applied to thesemiconductor wafer 1 as one example pattern to be inspected.

[0027] The beam expander 5 expands a laser beam to a certain size. Theexpanded laser beam L1 is converged in the vicinity 1 a of the pupil ofthe objective lens 11 with the lens 7, and thereafter used for Kohler'sillumination on the sample.

[0028] Further, the first plane mirror 4 a and the second plane mirror 4b are coupled to beam polarization mechanisms 40 a and 40 b in order tochange their angles. The beam expander 5 is also coupled to a beamexpander adjustment mechanism 50 capable of changing its focus position.Furthermore, a first beam splitter 30 a is provided after the beamexpander 5 for amplitude-splitting of a parallel pencil, and a secondbeam splitter 30 b separates the beam in two. One of the divided beamsenters into a beam profile observation camera 31 so that the shape ofthe beam is obtained. The other divided beam passes through aconvergence lens 33 and is converged on a beam spot positioning sensor32 so that a beam position displacement is detected.

[0029] A reflecting beam from the sample is detected with an imagesensor 13 via the objective lens 11, the polarization devices 10, thepolarization beam splitter 9, and an image formation lens 12, which arearranged vertically from above the sample. The polarization beamsplitter 9 reflects the beam, when the polarization direction of theleaser beam is parallel to its reflecting face. When the direction isperpendicular to the reflecting face, the splitter allows the beam to betransmitted therethrough. The laser beam used as a light source isoriginally a polarization laser, and the polarization beam splitter 9 isinstalled so as to reflect all the laser beams.

[0030] Meanwhile, the pattern to be inspected, which has been formed onthe wafer 1 through semiconductor processes, exhibits various shapes.Therefore, a reflecting beam from the pattern has various polarizationcomponents. The polarization devices 10 control the polarizationdirection of the laser lighting beam and reflecting beam so as to have afunction to arbitrarily adjust a polarization ratio of the lightingbeam. The function prevents uneven brightness of the reflecting beamcaused by pattern shapes or density difference from reaching the imagesensor 13. The polarization devices comprise, for example, a ½wavelength plate and a ¼ wavelength plate.

[0031] The image sensor 13 is, for example, a time delayed integrationsensor (TDI sensor), which outputs shading image signals in response tothe brightness (thick or thin) of the reflecting beam from thesemiconductor wafer 1 having one exemplary pattern to be inspected. AnA/D converter 14 converts the shading image signals 13 a obtained fromthe image sensor 13 to digital signals. In other words, the stage 2 isscanned while the semiconductor wafer 1 having one exemplary pattern tobe inspected is moved at a constant speed, so that a focus detectionsystem (not shown) always detects the position of the surface to beinspected in the direction of the Z axis. The stage 2 is therebycontrolled in the direction of the Z axis so that the space between theobjective lens 11 and the surface to be inspected is kept constant.Then, the image sensor 13 detects brightness information (shading imagesignals) of the pattern formed on the semiconductor wafer with highaccuracy.

[0032] The reference numeral 15 represents, for example, an 8-bit typegradation converter, which conducts logarithmic, exponential, andpolynomial transformations on digital image signals outputted from theA/D converter 14 so as to correct uneven image brightness caused byinterference between the laser beam and a thin film formed on thesemiconductor wafer 1 during the processes. A delay memory 16 stores anddelays output image signals from the gradation converter 15 for onecell, one chip or one shot constituting the semiconductor wafer 1 with ascanning width of the image sensor 13. A comparator 17 compares imagesignals outputted from the gradation converter 15 with image signalsobtained by the delay memory 16 to detect disparities as defects. Thecomparator 17 compares the detected image with the image that isoutputted from the delay memory 16 and delayed with an amountcorresponding to a cell pitch, etc. Coordinates such as arrangement dataon a semiconductor wafer 1 obtained based on design information areinputted with an input means 18 including a keyboard, a disk, etc., andthereby a CPU 19 creates and stores in a storage device 20 defectinspection data based on coordinates such as arrangement data on thesemiconductor wafer 1, whose comparison results by the comparator 17have been inputted.

[0033] The defect inspection data, if necessary, can be displayed on adisplay means 21 such as a display, and further outputted to an outputmeans 22 so that defect points can be observed, for example, with otherreview devices. The comparator 17 comprises, for example, a circuit forpositioning images, a differential image detection circuit of positionedimages, a disparity detection circuit for digitalizing differentialimages, and a feature extraction circuit for extracting areas andlengths, coordinates, and other factors from the digitalized outputs.

[0034] In addition, the configuration of the low coherent optical unit 6of the lighting optical machine is described. In general, the laser hascoherence properties, and laser-lighting on a wafer may be a cause forgenerating speckle noise from a circuit pattern. Thus, in the case oflaser-lighting, it is necessary to reduce coherence.

[0035] Either of temporal or spatial coherence can be reduced forreducing the coherence. In the present invention, a laser beam istwo-dimensionally scanned by two scanning mirror mechanisms 71 and 74,which are approximately orthogonal to each other and whose reflectingfaces revolve in the direction indicated by the arrow as shown in FIG.3., to reduce spatial coherence.

[0036] The low coherent optical unit 6 is described in detail by furtherreferring to FIG. 2. The laser beam L1 is emitted from the laser beamsource 3 and expanded to a certain size by the beam expander 5 to becomea parallel pencil, which is reflected by the scanning mirror mechanism71, converged with the lens 72, and then made to become a parallelpencil again with the lens 73. After the parallel pencil is reflected bythe scanning mirror mechanism 74, it is converged on the center 1 la ofthe objective lens with the lens 7. The mirrors of the scanning mirrormechanisms 71 and 74 are in conjugate positions relative to the surfaceof the wafer 1. The scanning mirror mechanisms 71 and 74 haveoscillating mirrors that revolve or oscillate with electric signals, andthe laser beam L1 is thereby two-dimensionally scanned on the pupil ofthe objective lens 11. Examples of the electric signals to be inputtedinto the scanning mirror mechanisms 71 and 74 include triangular wavesand sinusoidal waves, and variations of the frequency or amplitude ofthe inputted electric signals enables the scanning of various shapes onthe pupil 11 a of the objective lens 11.

[0037] As described above, the beam polarization mechanism and beamexpander adjustment mechanism are provided relative to the laserlighting optical system. Since the lighting optical mechanism is storedin the housing, an operator can adjust the beam without directlytouching the optical system and there is no fear that the beam wouldleak to the outside, resulting in safe operations. This allows theoperator to be free from operations in a narrow space, so that saferoperations are assured.

[0038] In addition, a beam spot positioning sensor or a camera forobserving beam profile is provided to automatically control the beampolarization mechanism and beam expander adjustment mechanism, so that astable beam can constantly be applied to an object to be measured.

EFFECT OF THE INVENTION

[0039] The present invention provides a lighting optical machine and adefect inspection system that are highly reliable and safe when a laserbeam is used as a light source.

[0040] All publications, patents and patent applications cited hereinare incorporated herein by reference in their entirety.

What is claimed is:
 1. A lighting optical machine comprising: a housing,wherein the housing accommodates a laser source, a beam polarizationmechanism having first and second plane mirrors enabling a beam emittedfrom the laser source to be reflected so that the beam travels in thedirection almost parallel to the beam emitted from the laser source, abeam expander for converting the beam to a parallel beam having a largercross-sectional area, and an objective lens, through which the parallelbeam is reduced and applied to the surface of a sample; a first controlmechanism for controlling the directions of the two plane mirrors of thebeam polarization mechanism with an electric signal; and a secondcontrol mechanism for controlling the focus position of the beamexpander with an electric signal.
 2. The lighting optical machineaccording to claim 1, wherein the housing further accommodates a firstbeam splitter for amplitude-splitting the parallel beam in the lightpassage from the beam expander to the objective lens, a second beamsplitter for further dividing in two the parallel beam reflected by thefirst beam splitter, a beam profile observation camera for observing thebeam intensity profile of the cross-section of one of the dividedparallel beams, a convergence lens for converging the other dividedparallel beam, and a beam spot positioning sensor for detecting theposition of a spot image converged with the convergence lens, and thelighting optical machine further comprising display means, providedoutside the housing, for displaying output signals from either one of orboth the beam profile observation camera and beam spot positioningsensor.
 3. A defect inspection system comprising: a housing, wherein thehousing accommodates a laser source, a beam polarization mechanismhaving first and second plane mirrors enabling a beam emitted from thelaser source to be reflected so that the beam travels in the directionalmost parallel to the beam emitted from the laser source, a beamexpander for converting the beam to a parallel beam having a largercross-sectional area, an objective lens, through which the parallel beamis reduced and applied to the surface of a sample, a first beam splitterfor amplitude-splitting the parallel beam in the light passage from beamexpander to the objective lens, a second beam splitter for furtherdividing in two the parallel beam reflected by the first beam splitter,a beam profile observation camera for observing the beam intensityprofile of the cross-section of a first parallel beam, one of thedivided beams, a convergence lens for converging a second parallel beam,the other of the divided beams, and a beam spot positioning sensor fordetecting the position of a spot image converged with the convergencelens; display means for displaying output signals of either one of orboth the beam profile observation camera and beam spot positioningsensor; a first control mechanism for controlling the directions of thetwo plane mirrors of the beam polarization mechanism with an electricsignal; a second control mechanism for controlling the focus position ofthe beam expander with an electric signal; an optical image observationmechanism for forming an enlarged image of the sample irradiated withthe second parallel beam; and an image comparison mechanism forcomparing images of two areas on the sample obtained by the opticalimage observation mechanism to detect a defect.
 4. A lighting opticalmachine comprising: a housing, wherein the housing accommodates a lasersource, a first plane mirror for reflecting a beam emitted from thelaser source to the direction approximately perpendicular to thetraveling direction of the beam, a second plane mirror for reflectingagain the beam reflected by the first plane mirror to the directionapproximately perpendicular to the traveling direction of the reflectedbeam to generate the beam traveling in the direction approximatelyparallel to the beam emitted from the laser source, a beam expander forconverting the beam to a parallel beam having a larger cross-sectionalarea, and an objective lens, through which the parallel beam is reducedand applied to the surface of a sample; a first control mechanism forcontrolling the directions of the first and second plane mirrors of thebeam polarization mechanism with an electric signal; and a secondcontrol mechanism for controlling the focus position of the beamexpander with an electric signal.
 5. The lighting optical machineaccording to claim 4, wherein the housing further accommodates a firstbeam splitter for amplitude-splitting the parallel beam in the lightpassage from the beam expander to the objective lens, a second beamsplitter for further dividing in two the parallel beam reflected by thefirst beam splitter, a beam profile observation camera for observing thebeam intensity profile of the cross-section of one parallel beam of thedivided beams, a lens for converging the other parallel beam of thedivided beams, and a beam spot positioning sensor for detecting theposition of a spot image converged with the lens, the lighting opticalmachine further comprising display means for displaying output signalsof either one of or both the beam profile observation camera and beamspot positioning sensor.
 6. A defect inspection system comprising: ahousing, wherein the housing accommodates a laser source, a first planemirror for reflecting a beam emitted from the laser source to thedirection approximately perpendicular to the traveling direction of thebeam, a second plane mirror for reflecting again the beam reflected bythe first plane mirror to the direction approximately perpendicular tothe traveling direction of the reflected beam to generate the beamtraveling in the direction approximately parallel to the beam emittedfrom the laser source, a beam expander for converting the beam to aparallel beam having a larger cross-section area, an objective lens,through which the parallel beam is reduced and applied to the surface ofa sample, a first beam splitter for amplitude-splitting the parallelbeam in the light passage from the beam expander to the objective lens,a second beam splitter for further dividing in two the parallel beamreflected by the first beam splitter, a beam profile observation camerafor observing the beam intensity profile of the cross-section of a firstparallel beam, one of the divided beams, a convergence lens forconverging a second parallel beam, the other of the divided beams, and abeam spot positioning sensor for detecting the position of a spot imageconverged with the convergence lens; display means for displaying outputsignals of either one of or both the beam profile observation camera andbeam spot positioning sensor; a first control mechanism for controllingthe directions of the two plane mirrors of the beam polarizationmechanism with an electric signal; a second control mechanism forcontrolling the focus position of the beam expander with an electricsignal; an optical image observation mechanism for forming an enlargedimage of the sample irradiated with the second parallel beam; and animage comparison mechanism for comparing images of two areas on thesample obtained by the optical image observation mechanism to detect adefect.